Have a 71 Chevelle, approx 3400 lbs w/355 sbc, Comp Cams 280H magnum cam, .480/.480 lift, .230 dur @ .050, .280 Adv dur, 106 cl, range is from 2000-6000 rpm, iron Vortec heads, Air Gap, Holley 750 dp, 3.73 posi rear. Now here is my problem, I had a 10" TCI Streetfighter 3000 stall converter in it and it ran like a scalded dog at WOT, however was slipping bad during normal slow traffic driving. So, I bought a Jegs 2300-2700 12" converter. After installing this converter, my car would barely idle and shifted extremely hard, yes I have a shift kit in it but it never shifted that hard. Tried driving it shifting it manually and it would only go into 2nd gear if I was at 2000 rpms or higher, then only into 3rd if at 2400 rpm or higher. What a major pain. Sometimes it wouldn't even shift into 2nd it would just rev up then go into gear. I called Jegs and they did not seem to know what the problem could be. They said I could return it if I wanted for a refund or another converter. Everything has been checked and rechecked for correct installation. No bent lines, full fluid, etc. Any thoughts on this problem before I return it?